520 bridge Pontoon W returns to Lake Washington

SEATTLE – Pontoon W – one of the 77 new State Route 520 bridge pontoons – is returning to Lake Washington Monday, Sept. 30, this time with six fewer columns than it had when last seen on the lake.

Earlier this month, SR 520 floating bridge project contractor Kiewit/General/Mason, a Joint Venture (KGM) towed the pontoon to the Manson Construction Company facility on the Duwamish River to remove six round concrete columns built on the pontoon last year. The pontoon previously had been at a Vigor dry dock for repairs.

“We’re happy to welcome Pontoon W back to Lake Washington,” said Dave Becher, Washington State Department of Transportation construction manager for the SR 520 Floating Bridge and Landings Project. “We’ve completed necessary repairs in the dry dock and removed columns that will be replaced on Lake Washington. Together, these repairs will ensure that the pontoon meets its 75-year design life, and we look forward to continue building the new SR 520 floating bridge.”

Last year rebar cages inside the six 58-foot-tall columns shifted slightly during a concrete pour. Crews will re-pour the columns on Lake Washington later this year. The removed columns will be dismantled, and the concrete and steel rebar will be recycled.

Because it was a construction issue, all costs associated with repairing the columns are the responsibility of KGM. No taxpayer money will be spent on the column repairs, and no time will be added to the project schedule.

Pontoon W will be towed Monday from the Manson site on the Duwamish River through the Lake Washington Ship Canal to Lake Washington. Along the way, the pontoon will require openings of six bridges – the Duwamish River Railroad Bridge, the lower level of the Southwest Spokane Street Swing Bridge, the Ballard Bridge, the Fremont Bridge, the University Bridge, and the Montlake Bridge. WSDOT expects the pontoon to arrive at the Hiram M. Chittenden Locks in Ballard at approximately 6 p.m. Monday, and pass through the Ballard Bridge after 7 p.m.

Once on the lake, Pontoon W will be moored at the east end of the existing floating bridge, where crews will add new rebar and pour new concrete. When complete, 10 round columns and two larger box columns will be used to support the highway on the new SR 520 floating bridge.

Pontoon W is one of two cross pontoons that will form the endpoints of the new floating bridge. It ultimately will be positioned at the easternmost end of the bridge, near the Medina shore. The other cross pontoon – Pontoon A – currently is located at the east end of the lake, where its box and round columns are being constructed. Pontoon A will form the westernmost end of the bridge between Madison Park and Laurelhurst.

As of September 2013, 32 of 77 pontoons for the new floating bridge are complete with additional cycles due from Aberdeen and Tacoma this fall and winter. Pontoon tracking details are posted online.